Various components used in computers generate heat that must be dissipated in order for the components to function properly. The heat generated by such computer components is typically dissipated using fans that draw or force ambient air across or through the components. In order to reduce power consumption and noise generation, the speeds of such fans are regulated relative to the needs of the computer in which the fans are provided. For example, the speed of a given fan may be controlled in relation to the temperature of a component that the fan is provided to cool. In some cases, federal regulations require that a given component not exceed a specified operating temperature.
Some cooling fans used within computers are microprocessor controlled. Although microprocessor control provides an advantage in terms of the precision with which the fan speed can be regulated, microprocessor control is not appropriate for every application. For instance, microprocessors may be inappropriate for cooling power supplies due to the relatively high cost of such microprocessors. Accordingly, alternative means have been used in the prior art to control computer fans.
In one solution, a power-dissipating device, such as a PNP transistor, is connected in series with the fan such that the amount of voltage that is delivered to the fan is reduced by the amount of voltage that is provided to the dissipating device. Although such a solution is viable, it is undesirable from a power consumption standpoint. Specifically, that solution is wasteful in that the same power is required to drive the fan irrespective of the speed at which the fan operates. A further disadvantage of that solution is that the range of fan operating speeds under such a control scheme is limited, as are the number of different speeds that the fan can be operated within that range.